The present invention relates generally to an unwind station of a web press, that is, to that portion within a web press where a roll of web material, typically paper, is held for unwinding as the web is fed into the press. More specifically, the invention relates to a mechanism for engaging and disengaging the shaft carrying the roll from a brake as the roll is loaded into or unloaded from the unwind station.
In a web press, web material is supplied to the press from a large roll positioned at one end of the press that is unwound as the material is fed through the various stations of the press. Such a roll can be quite heavy, typically weighing as much as 1800 (800 kg) pounds. Accordingly, the loading and positioning of a fresh roll into a press can be a formidable task. Most presses are therefore provided with a mechanism for lifting the roll into the unwind station of the press. Examples of such mechanisms are shown in U.S. Pat. No. 3,321,147 issued May 23, 1967 to Martin, and in U.S. Pat. No. 3,424,394 issued Jan. 28, 1969 to Moore.
In a typical unwind station, the roll is carried on a rotatably supported shaft. The shaft is not driven by the press, but is rotated as the web material is drawn into the press. Connected to one end of the shaft is an electromagnetic brake which is actuated and controlled electrically by the press control circuitry. The brake exerts a braking force on the shaft, and serves primarily to prevent overrunning of the roll as the press is stopped. The brake is also used at other times during the press operation, for example, to produce or maintain an appropriate amount of tension within the web.
Since the brake is coupled to the shaft which in turn supports the roll, the brake must be disconnected from the shaft as a used roll is lowered from the unwind station, and it must be reconnected once the new roll has been installed. Connection mechanisms for this purpose may typically include interlocking shafts with, for example, threaded collars for securing the connected shafts in place. Performing by hand the connection and disconnection operations during changing of a roll results in an increase in the non-productive time during which the press is shut down. Moreover, the potential is created for overlooking engagement or disengagement of the brake mechanism. In the case of a failure to disengage the brake prior to attempted lowering of the roll, the unsupported roll could be left attached to the brake, with the possibility of misalignment or other damage to the brake assembly. In the event connection of the brake following installation of a new roll is overlooked, operation of the press could result in the roll spinning in totally uncontrolled fashion.
What is needed, therefore, is a brake engagement and disengagement mechanism for the unwind station of a web press. Such a mechanism should require little or no direct action on the part of the press operator, thereby decreasing the amount of time necessary to change a roll, and reducing the possiblity of an overlooked connection or disconnection of the brake mechanism and the roll shaft. However, such a mechanism must be reliable to ensure that appropriate connection or disconnection is made.